1. Field of the Invention
The present invention relates to an apparatus and a method for demodulating subcarrier tag signal in radio frequency identification (RFID) reader. This work was supported by the IT R&D program of MKE/IITA [2008-F-052-01, The Development of next generation radio frequency identification (RFID) for Application of Individual Product Unit].
2. Description of Related Art
Generally, radio frequency identification (RFID) is a technology which uses radio frequencies to wirelessly communicate with a tag having unique identification information, thereby identifying, detecting, and managing objects, animals, and human beings with the tag attached. An RFID system consists of a plurality of electronic tags or transponder which are attached to objects or animals, and an RFID reader or an RFID interrogator for reading information from the tag or writing one into the tag.
The RFID system is divided into a mutual induction scheme and an electromagnetic wave scheme depending on a mutual communication scheme between the reader and the tag, divided into an active type and a passive type depending on whether the tag operates with self power, and divided into a long wave type, a mid wave type, a short wave type, and a microwave type.
Also, since the RFID reader communicating with the passive RFID tag is required to consecutively supply the passive RFID tag with transmission energy (TX CW) while receiving a tag signal, a great amount of a transmission energy (TX CW) component can leak to a receiver in the RFID unless separation of transmission/reception is sufficiently guaranteed.
The transmission energy (TX CW) component leaked to the receiver in the RFID reader may cause a DC-offset noise in a baseband of the RFID reader. This DC-offset noise can severely deteriorate the performance of the demodulation of the tag signal in the RFID reader. Consequently, the RFID reader may not successfully restore an original signal from the corrupted signal with the DC-offset noise.